1. File of the invention
The present invention relates to an optical module that implements a light-receiving device, typically a photodiode (PD), and a light-transmitting device, typically a laser diode (LD), within a common housing. In particular, the invention relates to an optical bi-directional module with a co-axial package.
2. Related Prior Arts
A bi-directional module, where the PD and the LD are implemented with a common package with the co-axial shape, has been well known in the field of the optical communication. Such a bi-directional module drives the LD with a relatively larger current, typically over several tens of milli-ampere; while, the PD converts a faint optical signal received thereby into a small photocurrent, typically several micro-amperes at most. Accordingly, the crosstalk may easily occur from the transmitter section including the LD to the receiver section including the PD.
Various techniques have been known in the field to reduce the crosstalk. A Japanese patent published as JP-2005-203553A has disclosed one of the techniques where the optical module electrically separates the ground for the LD and that for the PD by mounting the LD and the PD on respective and separate metal plates. Another Japanese patent published as JP 2006-041234A has disclosed an optical module in which the LD is mounted on the substrate, while, the PD is shielded by the ground plane formed in the back surface of the substrate. Still another Japanese patent published as JP 2006-253820A, whose counter United States patent application has been published as US20060210280A has disclosed an optical transceiver that installs the Tx unit, the Rx unit, and the timing adjustor in the single housing. The timing adjustor adjusts the timing of the Tx unit and the Rx unit so as not to coincide the rising or the falling of respective pulse signals.
The techniques disclosed in prior documents reduce the crosstalk by physical substances, namely, the plural ground plate, the shielding plate and the timing adjustor circuit; accordingly, the module is necessary to secure a space for such physical substances and specific components. Thus, the prior techniques are hard to make the optical module compact in physical dimensions thereof.